1. Field of the Invention
The present invention concerns an arrangement to transmit magnetic resonance signals that are acquired by local coils.
2. Description of the Prior Art
Modern magnetic resonance systems simultaneously acquire a number of magnetic resonance signals via local antennas that are placed on the patient. These local antennas are components of what is known as a “local coil”. The acquired magnetic resonance signals are pre-amplified, conducted away from a central region of the magnetic resonance system and supplied to a shielded receiver in order to be used therein for image processing.
The connection lines used for transmission are generally directed within a movable patient bed and are therefore several meters in length. The technical problems described below result due to the use of connection lines.
The cables exhibit attenuations in the frequency range of the magnetic resonance signals to be transmitted; these attenuations must be taken into account in designing the signal transmission path. For this purpose, a patient-proximal pre-amplification of the magnetic resonance signals and ensue before the transmission. This causes heat to be generated in proximity to the patient. To avoid such heat generations, low-attenuation cables are presently used for transmission but these have a large cable diameter and are correspondingly unwieldy.
Each local antenna forms an acquisition channel that has a connection cable associated with it for transmission of the magnetic resonance signal. An unwieldy cable bundle is likewise formed by the number of acquisition channels; the cable bundle is subjected to increased mechanical loads due to the movement of the patient bed, even given the use of cable plugs on the bed.
The problem of the cited cable bundle is aggravated by the fact that at least a part of is the cable bundle in part in the radio-frequency field of the magnetic resonance transmission antenna and therefore must contain sheath wave barriers. Due to the dimensions of such items, the cable bundle thickness is again additionally, significantly increased.
Previously used coaxial multiconductor plugs are expensive in the wiring process and unwieldy in use for the operating personnel.
Previously used pre-amplifiers must exhibit a high linearity of the amplifier characteristic curve over a large range in order to form low-distortion output signals. This requires a high power draw and thus produces high waste heat near the patient.
Presently broadband receivers are used that can receive magnetic resonance signals that emanate not only from hydrogen but also from other atoms. Such receivers have a transmission network that contains ferrite cores. Due to the ferrite cores, the receiver cannot be operated in the immediate environment of the static basic field of the magnetic resonance apparatus, such that long connection paths are necessary again that lead to the technical problems cited above.